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United States Patent |
6,257,207
|
Inui
,   et al.
|
July 10, 2001
|
Startup control apparatus of internal combustion engine and startup control
method
Abstract
A startup control apparatus of an internal combustion engine is provided
wherein when an engine starting capability determining device determines
that the engine can be successfully started even if driving of part of the
fuel injector valves is stopped during engine startup, the fuel injection
is stopped with respect to the part of the fuel injector valves. With this
arrangement, overshoot of the engine speed that would otherwise occur upon
the start of the engine can be suppressed, and unburned fuel components
can be prevented from being discharged, thus assuring improved exhaust gas
characteristics and improved fuel efficiency.
Inventors:
|
Inui; Toshio (Kyoto, JP);
Miyamoto; Katsuhiko (Kyoto, JP);
Hoshiba; Yoshiyuki (Kyoto, JP)
|
Assignee:
|
Mitsubishi Jidosha Kogyo Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
390309 |
Filed:
|
September 3, 1999 |
Foreign Application Priority Data
| Sep 04, 1998[JP] | 10-250861 |
Current U.S. Class: |
123/491; 123/480; 123/481; 701/113 |
Intern'l Class: |
F02D 041/06; F02D 041/02 |
Field of Search: |
123/481,305,491,494,179.16,179.21,480
701/103,104,113
|
References Cited
U.S. Patent Documents
4512320 | Apr., 1985 | Abe et al. | 123/682.
|
5746183 | May., 1998 | Parke et al. | 123/492.
|
5809973 | Sep., 1998 | Iida et al.
| |
5881694 | Mar., 1999 | Nakada | 123/305.
|
5979400 | Nov., 1999 | Nishide | 123/305.
|
5979413 | Nov., 1999 | Ohnuma et al. | 123/491.
|
Foreign Patent Documents |
0984147 A2 | Mar., 2000 | EP.
| |
Other References
Patent Abstracts of Japan--Abstract for JP 10-054272, published Feb. 24,
1998.
|
Primary Examiner: Yuen; Henry C.
Assistant Examiner: Vo; Hieu T.
Claims
What is claimed is:
1. A startup control apparatus of an internal combustion engine,
comprising:
a plurality of cylinders;
a plurality of fuel injector valves provided for the plurality of
cylinders, respectively;
a control unit comprising a fuel injected cylinder limiting device that
controls at least one of the fuel injector valves to limit an amount of
fuel injected into the corresponding cylinders during startup of the
internal combustion engine; and
an engine starting capability determining device capable of identifying a
number of fuel injector valves of less than all of the fuels injector
valves that are necessary for starting the engine, the engine being
started using only the fuel injector valves identified by the engine
starting capability determining device.
2. A startup control apparatus according to claim 1, wherein the fuel
injected cylinder limiting device stops at least one of the fuel injector
valves during startup of the internal combustion engine.
3. A startup control apparatus according to claim 1,
wherein said control unit further comprises an engine starting capability
determining device that determines whether the engine can be successfully
started by controlling the at least one of the fuel injector valves to
limit the amount of fuel injected during startup of the engine, and
wherein said control unit permits said fuel injected cylinder limiting
device to be activated when the engine starting capability determining
device determines that the engine can be successfully started.
4. A startup control apparatus according to claim 3, further comprising:
a temperature detecting device that detects a temperature of the engine;
and
wherein the engine starting capability determining device determines that
the engine cannot be successfully started if driving of the at least one
fuel injector valves is stopped during startup of the engine when the
temperature detected by the temperature detecting device is lower than a
first predetermined temperature.
5. A startup control apparatus according to claim 4, wherein the
temperature detecting device comprises:
a water temperature sensor provided on a main body of the engine and
adapted to detect a coolant temperature of the engine, and wherein the
engine starting capability determining device determines whether the
engine can be successfully started based on the coolant temperature
detected by the water temperature sensor.
6. A startup control apparatus according to claim 4, wherein the
temperature detecting device comprises:
an ambient temperature sensor that detects an ambient temperature, and
wherein the engine starting capability determining device determines
whether the engine can be successfully started based on the ambient
temperature detected by the ambient temperature sensor.
7. A startup control apparatus according to claim 4, wherein the control
unit stops operating the fuel injected cylinder limiting device when the
temperature detected by the temperature detecting device is higher than a
second predetermined temperature that is set to be higher than the first
predetermined temperature.
8. A startup control apparatus according to claim 3, further comprising:
an engine speed determining device that determines whether a rotating speed
of the internal combustion engine reaches a predetermined speed;
wherein the control unit comprises a startup control device that causes the
fuel injector valves to sequentially inject the fuel into the respective
cylinders during engine startup; and
wherein the control unit activates the startup control device when the
engine speed determining device determines that the rotating speed of the
engine does not reach the predetermined speed within a predetermined
period after the fuel injected cylinder limiting device is activated.
9. A startup control apparatus of an internal combustion engine according
to claim 3, further comprising:
a cylinder identifying device that identifies the cylinders;
wherein the control unit permits the fuel injected cylinder limiting device
to be activated after the engine starting capability determining device
determines that the engine can be successfully started and the cylinder
identifying device completes identification of the cylinders.
10. A startup control apparatus according to claim 9, wherein said fuel
injected cylinder limiting device stops driving of alternate ones of the
fuel injector valves after the fuel injected cylinder limiting device is
activated.
11. A startup control apparatus according to claim 1, wherein said fuel
injector valves are provided on a main body of the internal combustion
engine, such that each of the fuel injector valves directly injects the
fuel into a corresponding one of the cylinders.
12. A startup control method for controlling startup of an internal
combustion engine including a plurality of cylinders, and a plurality of
fuel injector valves respectively provided for the cylinders comprising:
detecting a start of cranking of the internal combustion engine;
identifying the cylinders after the start of cranking of the engine is
detected;
after cylinder identification is completed, determining whether the engine
can be successfully started by driving less than all of the fuel injector
valves that are timed to inject fuel into cylinders, based on temperature
information of the engine; and
controlling driving of the fuel injector valves to limit fuel injection
based on whether it is determined that the engine can be successfully
started by driving less than all of the fuel injector valves.
13. A startup control method according to claim 12, wherein the controlling
includes stopping the driving of at least one of the fuel injector valves
when it is determined that the engine can be successfully started by
driving less than all of the fuel injector valves.
14. A startup control method according to claim 13, further comprising:
determining whether a rotating speed of the internal combustion engine
reaches a predetermined speed after the driving of the at least one of the
fuel injector valves is stopped; and
sequentially driving the fuel injector valves of all of the cylinders
according to a predetermined fuel injection timing, without stopping
driving of said at least one of the fuel injector valves, if it is
determined after a predetermined time that the rotating speed of the
engine does not reach the predetermined speed.
15. A startup control method according to claim 13, wherein driving of the
fuel injector valves is stopped with respect of one of the cylinders upon
completion of cylinder identification, and at least alternate ones of the
cylinders that follow the one of the cylinders, when it is determined that
the engine can be successfully started by driving less than all of the
fuel injector valves.
16. A startup control method according to claim 12, further comprising:
detecting a temperature of coolant within the engine; and
comparing the temperature of the coolant to a first predetermined
temperature, wherein the fuel injector valves of all of the cylinders are
sequentially driven according to a predetermined fuel injection timing,
without stopping driving of any of the fuel injector valves, when the
temperatures of the coolant is lower than the first predetermined
temperature.
17. A startup control method according to claim 16, further comprising:
comparing the temperature of the coolant to a second predetermined
temperature, wherein the fuel injector valves of all of the cylinders are
sequentially driven according to a predetermined fuel injection timing,
without stopping driving of any of the fuel injector valves, when the
temperature of the coolant is higher than the second predetermined
temperature that is higher than the first predetermined temperature.
18. A startup control method according to claim 12, further comprising:
detecting an ambient temperature proximate to the engine; and
comparing the temperature to a predetermined ambient temperature, wherein
the fuel injector valves of all of the cylinders are sequentially driven
according to a predetermined fuel injection timing, without stopping
driving of any of the fuel injector valves, when the ambient temperature
detected is lower than the predetermined ambient temperature.
Description
FIELD OF THE INVENTION
The present invention relates to apparatus and method for controlling
startup of an internal combustion engine including a plurality of
cylinders.
BACKGROUND OF THE INVENTION
In internal combustion engines including a plurality of cylinders and a
fuel injector valve for each of the cylinders, for example, a multi-point
fuel injection (MPI) engine with a fuel injector valve provided at an
intake port of each cylinder, and an in-cylinder injection type internal
combustion engine with a fuel injector valve for injecting fuel directly
into a combustion chamber of each cylinder, an electronic control unit
(ECU) operates to detect the start of cranking of the engine upon receipt
of an ON signal from a cranking switch, and then to carry out cylinder
identification based on signals received from a crank angle sensor and
others. Once the cylinder identification is completed, the ECU drives the
fuel injector valve of each cylinder with suitable timing so as to start
the engine. In this operation, the ECU sets the driving period or duration
of the fuel injector valve so that the amount of fuel ejected from the
fuel injector valve during engine startup is larger than that ejected
while the engine is idling after warm-up thereof. The amount of fuel
ejected from the fuel injector valve during engine startup is relatively
large for the reason as follows: where the engine is started in the cold
state, and vaporization of the fuel injected into the cylinder is delayed
due to a low temperature within the cylinder, for example, a sufficient
amount of fuel required for combustion needs to be present around the
spark plug so as to fire an air-fuel mixture without fail.
However, if the amount of the fuel is relatively large during startup of
the engine as described above, the fuel injection amount per cylinder is
increased, thus causing excessive racing of the engine upon combustion, or
overshoot of the engine speed. Also, since the total amount of the fuel
injected into the internal combustion engine as a whole is increased
during startup of the engine, the fuel efficiency may be lowered, and
exhaust gas characteristics may deteriorate due to increased unburned fuel
components that were not used for combustion and that were eventually
dispelled in exhaust gas.
As disclosed in laid-open Japanese Patent Publication No. 10-54272, for
example where the water temperature is equal to or lower than a
predetermined level after completion of cylinder identification, the fuel
injection is halted for a period of time corresponding to two strokes, so
that the temperature within the combustion chamber is increased due to a
compression effect of the internal combustion engine, and the fuel
injector valves are subsequently actuated.
The technique disclosed in the above publication, wherein the fuel
injection is stopped for a period of two strokes after cylinder
identification is completed, is advantageous in terms of the fuel
efficiency and exhaust gas characteristics, as compared with the known
technique of increasing the fuel amount. It is, however, difficult to
achieve the desired temperature in the combustion chamber by utilizing the
compression effect of the internal combustion engine, and the amount of
the fuel injected after stopping the fuel injection for a period of two
strokes must be determined taking account of the case where the
temperature in the combustion chamber was not sufficiently increased, as
in the known method of increasing the fuel amount. Also, since the fuel is
injected into all of the cylinders in a specific sequence after a halt of
the fuel injection, the total amount of fuel injection in the internal
combustion chamber as a whole tends to be large during engine startup.
Thus, there is a plenty of room for improvements in the above-described
known methods, which are to be made for suppressing overshoot of the
engine speed, and deterioration of exhaust gas characteristics and fuel
efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a startup
control apparatus of an internal combustion engine which can overcome the
above and other shortcomings of conventional apparatuses and that can
suppress overshoot of the engine speed, and avoid deterioration of exhaust
gas characteristics and fuel efficiency.
To accomplish the above and other objects, the present invention provides a
startup control apparatus of an internal combustion engine, which
comprises a plurality of cylinders, a plurality of fuel injector valves
respectively provided for the plurality of cylinders, and a control unit
comprising a fuel injected cylinder limiting device that stops driving of
at least one of the fuel injector valves that are timed to inject fuel
into the cylinders, during startup of the internal combustion engine.
With the above arrangement, the total amount of the fuel injected into all
of the cylinders during startup of the internal combustion engine can be
reduced, thereby suppressing overshoot of engine rotation or engine speed,
while assuring improved exhaust gas characteristics and fuel efficiency.
In one preferred form of the startup control apparatus as described above,
the control unit further comprises an engine starting capability
determining device that determines whether the engine can be successfully
started even if driving of at least one of the fuel injector valves in
fuel injection timing is stopped during startup of the engine, and the
control unit permits the fuel injected cylinder limiting device to be
activated when the engine starting capability determining device
determines that the engine can be successfully started. With this
arrangement, the internal combustion engine can be smoothly started with
high reliability.
The startup control apparatus as described just above may further include a
temperature detecting device that detects a temperature of the engine. In
this case, the engine starting capability determining device determines
that the engine cannot be successfully started if driving of at least one
of the fuel injector valves in fuel injection timing is stopped during
startup of the engine, when the temperature detected by the temperature
detecting device is lower than a first predetermined temperature. With
this arrangement, the fuel injected cylinder limiting device is actuated
based on the result of a determination by the engine starting capability
determining device, and therefore the internal combustion engine can be
smoothly started with high stability and reliability.
In the above case, the temperature detecting device preferably takes the
form of a water temperature sensor provided on a main body of the engine
and adapted to detect a coolant temperature of the engine, or an ambient
temperature sensor that detects an ambient temperature, and the engine
starting capability determining device determines whether the engine can
be successfully started, based on the outputs of these sensors.
In the startup control apparatus including the temperature detecting device
as described above, the control unit may preferably stop operating the
fuel injected cylinder limiting device when the temperature detected by
the temperature detecting device is higher than a second predetermine
temperature that is set to be higher than the first predetermined
temperature. Thus, the engine can be started with high stability.
In the above preferred form of the invention, the startup control apparatus
may preferably include an engine speed determining device that determines
whether the rotating speed of the internal combustion engine reaches a
predetermined speed, and the control unit may include a startup control
device that causes the fuel injector valves to sequentially inject the
fuel into the respective cylinders during engine startup. In this case,
the control unit activates the startup control device when the engine
speed determining device determines that the rotating speed of the engine
does not reach the predetermined speed after the fuel injected cylinder
limiting device is activated. Thus, the engine can be started with high
stability.
In the above preferred form of the invention, the startup control apparatus
may further include a cylinder identifying device that identifies the
cylinders, and the control unit may permit the fuel injected cylinder
limiting device to be activated after the engine starting capability
determining device determines that the engine can be successfully started
and the cylinder identifying device completes identification of the
cylinders. In this case, the fuel injected cylinder limiting device
preferably stops driving of alternate ones of the fuel injector valves in
fuel injection timing after the fuel injected cylinder limiting device
starts being activated. This arrangement makes it possible to suppress
overshoot of engine rotation, and avoid deterioration of exhaust gas
characteristics and fuel efficiency, while assuring high engine starting
capability.
In another preferred form of the starting control apparatus of the
invention, the fuel injector valves are provided on a main body of the
internal combustion engine, such that each of the fuel injector valves
directly injects the fuel into a corresponding one of the cylinders. In
this case, the fuel injection into each cylinder can be accurately
controlled, thus surely suppressing overshoot of engine rotation and
avoiding deterioration of exhaust gas characteristics and fuel efficiency.
According to another aspect of the present invention, there is provided a
startup control method for controlling startup of an internal combustion
engine including a plurality of cylinders, and a plurality of fuel
injector valves respectively provided for the cylinders, which method
comprises the steps of: detecting a start of cranking of the internal
combustion engine; identifying the cylinders after the start of cranking
of the engine is detected; after cylinder identification is completed,
determining, based on temperature information of the engine, whether the
engine can be successfully started even if driving of at least one of the
fuel injector valves that are timed to inject fuel into cylinders is
stopped; and stopping driving of at least one of the fuel injector valves
when it is determined that the engine can be successfully started. With
this method, the total amount of the fuel injected into all of the
cylinders during startup of the internal combustion engine can be reduced,
thereby suppressing overshoot of engine rotation or engine speed, while
assuring improved exhaust gas characteristics and fuel efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed
description given hereinbelow and the accompanying drawings which are
given by way of illustration only, and thus are not limitative of the
present invention, and wherein:
FIG. 1 is a block diagram schematically showing the construction of a
startup control apparatus of an internal combustion engine according to
one embodiment of the present invention;
FIG. 2 is a block diagram schematically showing the construction of the
internal combustion engine that employs the startup control apparatus of
the present invention;
FIG. 3 is a flowchart showing a control routine to be executed by the
startup control apparatus of the internal combustion engine according to
the present invention;
FIGS. 4(A) and 4(B) are graphs showing the effects of the startup control
apparatus of the internal combustion engine, wherein FIG. 4(A) shows the
effect of the startup control apparatus of the present invention, and FIG.
4(B) shows the effects of a conventional startup control apparatus;
FIGS. 5(A) and 5(B) are graphs showing the effects of the startup control
apparatus of the internal combustion engine, wherein FIG. 5(A) is a graph
useful for comparing the startup control apparatus of the present
invention with the conventional startup control apparatus, and FIG. 5(B)
is a graph useful for explaining control performed by the startup control
apparatus of the present invention when it is found difficult to start the
engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
One preferred embodiment of the present invention will be described with
reference to the drawings, although modifications to this embodiment will
be readily appreciated by those of ordinary skill.
The internal combustion engine of the present embodiment is an in-cylinder
injection type engine for a motor vehicle, wherein fuel is injected
directly into each engine cylinder to provide an air-fuel mixture that is
ignited by a spark plug for combustion thereof.
More specifically, as illustrated by FIG. 2, a cylinder head of the engine
1 is provided with a spark plug 3 and a fuel injector valve 6 for each
engine cylinder 3, such that the fuel injector valve 6 is directly open or
exposed to a combustion chamber 5 defined in the cylinder. The spark plug
3 is driven by a spark plug coil 4A, and the fuel injector valve 6 is
driven by a driver 6A. A piston 8 coupled to a crankshaft 7 is mounted in
the cylinder 3. A hemispherical cavity or recess 9 is formed in the top
face of the piston 8.
The cylinder head 2 includes an intake port 11 that communicates with the
combustion chamber 5 via an intake valve 10, and an exhaust port 13 that
communicates with the combustion chamber 4 via an exhaust valve 12. The
intake port 11 extends upwards from the combustion chamber 5 in a
substantially vertical direction, and cooperates with the cavity 9 formed
in the top face of the piston 8 to produce a reverse tumble flow of intake
air within the combustion chamber 5.
A water jacket 15 disposed on the outer periphery of the cylinder 6 is
provided with a water temperature sensor 16 for detecting a coolant
temperature that varies with the engine temperature. The water temperature
sensor 16 functions as one type of temperature detecting device for
detecting the engine temperature in the present embodiment. The crankshaft
7 is equipped with a crank angle sensor 17 that generates a signal at a
certain crank angle position, and each of camshafts 18, 19 for driving the
intake valve 10 and exhaust valve 12 is equipped with a cylinder
identification sensor (cam sensor) 20 that generates a cylinder
identification signal indicative of the position of the relevant camshaft.
The cylinder identification sensor 20 functions as one type of cylinder
identification device in the present embodiment.
The intake system principally consists of an air cleaner 21, intake pipe
22, throttle body 23, surge tank 24, and an intake manifold 25, which are
arranged in this order from the upstream side. The intake port 11 is
connected to the downstream end portion of the intake manifold 25. The
exhaust system principally consists of an exhaust manifold 26 having the
exhaust port 12, and exhaust pipes 27, 28, which are arranged in this
order from the upstream side, with an exhaust gas purifying catalyst 29
interposed between the exhaust pipe 27 and the exhaust pipe 28.
The throttle body 23 of the intake system includes a throttle valve 30, and
a small-diameter first air bypass path (for controlling the idling speed)
31 that bypasses the throttle valve 30. A first air bypass valve 32 is
mounted in the first air bypass path 31. In addition, a large-diameter
second air bypass path 33 is provided which bypasses the throttle body 23,
and a second air bypass valve 34 is mounted in the second air bypass path
33. The idling speed may be controlled by controlling the opening of the
first air bypass valve 32, while a large amount of intake air may be
introduced into the cylinder 3 by controlling the opening of the second
air bypass valve 34.
A large-diameter exhaust gas recirculation port (EGR port) 14 diverges from
the exhaust port 13, to be connected to a part of the throttle body 23
(right under the surge tank 24) through an EGR pipe 35. An EGR valve 36 of
a stepper motor type, for example, is provided in the middle of the EGR
pipe 36, for controlling the exhaust gas recirculation amount (EGR
amount).
An air flow sensor 37 for detecting the amount of intake air is located
right downstream of the air cleaner 21, and a throttle position sensor 38
for detecting the throttle opening is provided in the vicinity of the
throttle valve 30. In the throttle body 23 is also provided an idle switch
39 that detects the full closed state of the throttle valve 30 to generate
an idle signal. Also, an O.sub.2 sensor 40 is provided in the exhaust
manifold 26 for detecting whether the air/fuel ratio is on the rich or
lean side relative to the stoichiometric ratio.
A fuel supply system for the engine 1 will be now described in detail.
Initially, fuel in a fuel tank 41 is pressurized by a low pressure fuel
pump 42 of the motor-driven type, and then fed to a high pressure fuel
pump 46 through a low pressure feed pipe 43. Here, the high pressure fuel
pump 46 is driven by the engine 1 in association with rotation of the
camshaft 18. The high pressure fuel discharged from the high pressure fuel
pump 46 is delivered from the high-pressure feed pipe 47 into each fuel
injector valve 6 through a delivery pipe 48.
A low pressure regulator 45 is connected to the low pressure feed pipe 43
via a return pipe 44, and serves to control the pressure of the fuel in
the low pressure feed pipe 43 to a predetermined low pressure level (for
example, about 0.3 to 0.4 MPa). Also, a high pressure regulator 50 is
connected to the delivery pipe 48 via a return pipe 49, and serves to
control the pressure of the fuel in the delivery pipe 48 to a
predetermined high pressure level (for example, about 2 to 7 MPa).
In addition, a fuel pressure selector valve 51 is provided in the
high-pressure regulator 40. When the selector valve 51 is placed in its
open position, the fuel in the return pipe 49 is released, thereby to
control the fuel pressure of the delivery pipe 48 to a desired low level.
A return pipe 52 is also provided which returns redundant fuel in the high
pressure fuel pump 46 back to the fuel tank 41.
An electronic control unit (ECU) 60 is provided for controlling the
operations of respective engine control elements, including the spark plug
4, fuel injector valve 6, first air bypass vale 32, second air bypass
valve 34, EGR valve 36, low pressure fuel pump 42, and the fuel pressure
selector valve 51. The ECU 60 includes an input/output device, storage
device for storing control programs, control maps and others, central
processing unit (CPU), timer, counter, and so forth, and controls the
above-indicated engine control elements, based on detected information
from various sensors as described above, position information from a key
switch 53, ambient temperature information detected by an ambient
temperature sensor 54, and so on. Since the ambient temperature detected
by the ambient temperature sensor 54 has an influence on the engine
temperature, this sensor 54 serves as one type of temperature detection
device for detecting the engine temperature in the present embodiment.
The engine of the present embodiment, in particular, is an in-cylinder
injection type engine, in which the fuel injection into the combustion
chamber 5 can be carrier out in free timing, i.e., at any point in each
combustion cycle. Thus, the fuel is mainly injected during a suction
stroked so as to permit premixed combustion, or mainly injected during a
compression stroke so as to permit stratified charge combustion utilizing
the reverse tumble flow as described above. To achieve the premixed
combustion, the engine operates in a selected one of several combustion
modes, including a stoichiometric operation mode in which the air-fuel
ratio is held in the vicinity of the stoichiometric ratio through feedback
control based on information detected by the O.sub.2 sensor 40, an
enrichment operation mode in which the air-fuel ratio is controlled to be
richer than the stoichiometric ratio, and a normal lean operation mode in
which the fuel injection occurs during a suction stroke so as to control
the air-fuel ratio to be leaner than the stoichiometric ratio. To achieve
the stratified combustion, the engine operates in an extremely lean
operation mode in which the fuel injection occurs during a compression
stroke so as to control the air-fuel ratio to be much leaner than the
stoichiometric ratio.
The ECU 60 selects one of the engine operation modes according to a
predetermined map, based on the engine speed Ne and the average effective
pressure Pe representing the engine load condition. Generally, the ECU 60
selects the extremely lean operation mode when the engine speed Ne and the
average effective pressure Pe are small, and selects the normal lean
operation mode, stoichiometric operation mode, and the enrichment
operation mode in this order as the engine speed Ne and the average
effective pressure Pe increase.
The ECU 60 selects the stoichiometric operation mode when the required
engine load is large, and selects the enrichment operation mode when the
required engine load is even larger. The ECU 60 selects the normal lean
operation mode when the required engine load is small, and selects the
extreme lean operation mode when the required engine load is even smaller.
The engine speed Ne is calculated based on information detected by the
crank angle sensor 17, and the average effective pressure Pe is calculated
based on the engine speed Ne and the throttle opening (corresponding to
the degree of depression of an accelerator pedal) that is detected by the
throttle position sensor 38.
Based on the engine speed N3 and the average effective pressure Pe thus
calculated, the ECU 60 sets a target air-fuel ratio, fuel injection
timing, ignition timing, EGR amount and others, according to a map
established for each of the operating modes. Also, the ECU 60 sets the
amount of fuel to be injected, based on the target air-fuel ratio and the
amount of intake air detected by the air flow sensor 37, and controls the
fuel injector valve 6, ignition plug 4, EGR valve 36 and so forth.
As shown in FIG. 1, the ECU 60 has a startup control device of the internal
combustion engine 61 for performing engine control during engine startup,
and a normal control device 62 for performing engine control during normal
running of the vehicle.
The normal control device 62 includes an engine operation mode selecting
device 62A for selecting one of the above-indicated engine operation modes
based on the calculated engine speed Ne and average effective pressure Pe,
and a target air-fuel ratio setting device 62B for setting the target
air-fuel ratio for each engine operation mode based on the engine speed Ne
and average effective pressure Pe. The normal control device 62 further
includes devices for setting the fuel injection amount (open-valve
duration of the fuel injector valve), the fuel injection timing (point of
time at which the fuel injector valve is opened), spark ignition timing,
the EGR amount (degree of opening of the EGR valve), and the openings of
the air bypass valves (ABV) 32, 34, respectively. Namely, the normal
control device 62 includes a fuel injection amount setting device, fuel
injection timing setting device, spark ignition timing setting device, EGR
amount setting device, and the ABV opening setting devices. Based on the
outputs of these devices, the ECU 60 is adapted to control the fuel
injector valve 6, spark plug 4, EGR valve 36, air bypass valves 32, 34,
and other components.
The startup control devices 61, on the other hand, performs control from a
point of time when the vehicle is started, i.e., when the key switch 53
(or cranking switch) is placed in the ON state, to a point of time when
complete combustion takes place in the combustion chamber of each
cylinder. The judgment as to whether complete combustion takes place in
the combustion chamber is made by determining whether the engine speed Ne
has reached a predetermined speed Ne1 or not.
More specifically, a starter motor starts rotating the engine when the
cracking switch 53 is turned ON, but the rotating speed of the engine is
extremely low when the engine is only rotated by the starter motor. Once
completion combustion takes place in the combustion chamber, however, the
engine speed Ne is increased due to the combustion energy, to exceed the
predetermined speed (startup completion speed) Ne1. Thus, the engine is
judged as being in the complete combustion state when the engine speed Ne
exceeds the predetermined speed Ne1.
The startup control is performed only for an extremely short time (about
several seconds). If appropriate control is not performed during engine
startup, however, overshoot of engine rotation may occur immediately after
the startup period, or a large amount of unburned fuel components, such as
hydrocarbon (HC), is discharged from the combustion chamber, resulting in
deterioration of exhaust gas characteristics and reduced fuel efficiency.
In the present embodiment, therefore, the startup control device 61 is
designed to implement startup control operations so as to overcome these
problems.
As shown in FIG. 1, the startup control device 61 includes a starting
target air-fuel ratio setting device 61A for setting a target air-fuel
ratio during engine startup based on the engine coolant temperature
detected by the water temperature sensor 18, a fuel injected cylinder
limiting device 61B for injecting the fuel into a limited number of
cylinders selected from a plurality of cylinders (four cylinders in the
present embodiment) originally installed on the vehicle, under certain
conditions during engine startup, and a fuel pressure control device 61C
for controlling the low pressure fuel pump 42 and the fuel pressure
selector valve 51.
The starting target air-fuel ratio setting device 61A sets a target
air-fuel ratio during engine startup, to be richer than the stoichiometric
air-fuel ratio, thereby ensuring that the spark plug 4 fires or ignites an
air-fuel mixture without fail. The starting target air-fuel ratio is
determined based on the coolant temperature. Namely, the starting target
air-fuel ratio is set to be richer as the coolant temperature is lower.
This is because the fuel is less likely to be evaporated upon start of the
engine due to a low temperature in the combustion chamber, and the startup
time is prolonged and the spark plug smolders if the fuel injection amount
is equivalent to that of the engine that has been warmed up, which tends
to cause a failure of the spark plug to fire the fuel-air mixture.
Accordingly, the fuel injection amount is increased as the temperature of
the combustion chamber (or the coolant temperature) is lower, so that an
increased amount of fuel is evaporated so as to enable the spark plug to
fire or ignite the fuel-air mixture.
The fuel injected cylinder limiting device 61B restricts or inhibits the
operations of selected fuel injector valves 6 under certain conditions
during engine startup. For example, if certain conditions are satisfied
after cylinder identification is completed based on detection signals of
the cylinder identification sensors (cam angle sensors) 20, the cylinder
limiting device 61B only permits fuel injection into alternate ones of the
cylinders.
More specifically described, in the case of the four-cylinder engine as in
the present embodiment, the fuel is injected from the fuel injector valves
6 into the first, third, fourth and second cylinders in this order during
normal running of the vehicle after the startup period. During the startup
period, on the other hand, if the first cylinder is determined as a
cylinder into which the fuel can be timely injected upon completion of
cylinder identification, the fuel is initially injected into the first
cylinder, and the fuel injection into the third cylinder is stopped. The
fuel is then injected into the fourth cylinder in the same manner with the
first cylinder, and the fuel injection into the second cylinder is stopped
in the same manner with the third cylinder.
When the fuel can be timely injected into the third cylinder immediately
after completion of cylinder identification, the fuel is initially
injected into the third cylinder, followed by inhibition of fuel injection
into the fourth cylinder, and then injected into the second cylinder,
followed by inhibition of fuel injection into the first cylinder.
The number of cylinders into which the fuel is injected is limited during
engine startup by the fuel injected cylinder limiting device 61B, under
the following conditions: (1) the engine coolant temperature WT detected
by the water temperature sensor 18 is within a certain range
(WT1.ltoreq.WT.ltoreq.WT2), (2) the ambient temperature AT detected by the
ambient temperature sensor 54 is within a certain range (AT 1.ltoreq.AT),
(3) the engine speed Ne calculated based on the detected information of
the crank angle sensor 17 is equal to or lower than the predetermined
speed Ne1 (that indicates the finish of the startup period, (4) the time
elapsed after the commencement of cranking is within a certain period of
time (the timer value T of the timer 55 that starts measuring upon the
commencement of cranking is equal to or smaller than T1, or T.ltoreq.T1).
The startup control device 61 includes a control condition judging device
(or starting capability judging device) 61D that determines whether these
conditions (1) to (4) are satisfied or not. If the control condition
judging device 61D determines that all of these conditions (1) to (4)
(among which the conditions (1) and (2) relate to the engine temperature)
are satisfied, the number of cylinders into which the fuel is injected is
limited by the starting fuel injected cylinder limiting device 61B.
The above control for limiting the number of cylinders into which the fuel
is injected during engine startup needs to be performed so as to suppress
overshoot of the engine speed and deterioration of exhaust gas
characteristics immediately after the startup period, and also ensure that
the engine is started without fail during the startup period.
As one of the control conditions (for determining the engine starting
capability when the number of fuel injected cylinders is limited), the
lower limit value WT1 is established for the engine coolant temperature WT
that is generally considered to be proportional to the engine temperature.
If the coolant temperature WT is equal to or higher than the lower limit
value WT1, the control for limiting the number of cylinders subjected to
fuel injection may be performed, namely, the fuel may be injected into
selected cylinders. If the coolant temperature WT1 falls below the lower
limit value WT1, the control for limiting the number of fuel injected
cylinders may deteriorate the engine starting capability, and therefore
the fuel is injected into all of the existing cylinders in a certain
sequence under normal startup control, without performing the control for
limiting the number of fuel injected cylinders.
Where the ambient temperature AT is extremely low, the engine starting
capability may deteriorate under the control of limiting the number of
fuel injected cylinders, even if the coolant temperature WT is not lowered
below the lower limit value WT1. As another engine starting capability
condition, the lower limit value AT1 is established for the ambient
temperature AT, and if the ambient temperature AT falls below the lower
limit value AT1, the fuel is injected into all of the cylinders in a
certain sequence under normal startup control.
Where the engine coolant temperature WT is sufficiently high (in general,
when the engine is re-started before being cooled down), the starting
target air-fuel ratio setting device 61A does not set the starting target
air-fuel ratio to be far richer than the stoichiometric ratio, thus
eliminating the need to particularly suppress overshoot of the engine
speed or avoid deterioration of exhaust gas characteristics upon
completion of the startup control operation. As another control condition,
therefore, the upper limit value WT2 of the coolant temperature WT is
established, and, if the coolant temperature WT exceeds the upper limit
value WT2, the fuel is injected into all of the cylinders in a certain
sequence under normal startup control.
The above-described condition (3) is used for determining whether the
engine has been started or not. Namely, if the engine speed Ne exceeds the
predetermined speed Ne1 (that indicates the finish of the engine startup
period), the fuel control for enriching the air-fuel ratio during engine
startup is terminated. At this point of time, the engine does not suffer
any longer from overshoot of the engine speed and deterioration of exhaust
gas characteristics, and therefore the above control for limiting the
number of fuel injected cylinders is terminated, and replaced by a normal
control operation in which the fuel is injected into all of the cylinder
in a certain sequence.
Where the condition (4) is satisfied, namely, where the engine speed Ne
does not exceed the predetermined speed (that indicates the finish of the
engine startup) even after a certain period of time elapses (timer value
T>T1), it is found difficult to start the engine under the control for
limiting the number of fuel injected cylinders. In this case, the control
for limiting the number of fuel injected cylinders is terminated, and the
normal startup control is performed under which the fuel is injected into
all of the existing cylinders in a certain sequence, to ensure that the
engine can be started without fail.
When the key switch 53 is placed on the ON state (namely, the cranking
switch is turned on), the fuel pressure control device 61C actuates the
lower pressure fuel pump 42, and places the fuel pressure selector valve
51 in the open state so as to release the fuel. Upon a lapse of a
predetermined time after the commencement of cranking, the fuel pressure
control device 61C places the fuel pressure selector valve 51 in the
closed state, and subsequently increases the fuel pressure by means of the
high pressure fuel pump 46. Thus, vapor is discharged from the delivery
pipe 48 by opening the fuel pressure selector valve 51 upon start of the
engine.
The startup control device of the internal combustion engine, as one
embodiment of the present invention, is constructed as described above and
is thus adapted to execute a startup control routine as shown in the
flowchart of FIG. 3 by way of example.
The control routine is initiated when the key switch 53 (or cranking
switch) is turned on, and step S10 is executed to store current engine
operating states received from various sensors. Step S20 is then executed
to determine whether cylinder identification has been carried out, based
on information from the cylinder identification sensors 20. If the
cylinder identification has not been completed, no fuel injection is
conducted in step S30. If the cylinder identification has been completed,
judgments on the control conditions of S40 to S70 are made as follows.
In step S40, it is determined whether the engine coolant temperature WT
detected by the water temperature sensor 17 is within a predetermined
range (WT1.ltoreq.WT.ltoreq.WT2). If the coolant temperature WT is lower
than the lower limit value WT1 (the first predetermined temperature), the
engine temperature may be excessively low, and the engine starting
capability may deteriorate if the fuel is selectively injected into only a
limited number of cylinders. In this case, therefore, the control flow
goes to step S90 to inject the fuel into all of the cylinders in a certain
sequence.
Upon start of the engine, the enrichment operation mode is selected so as
to ensure that a spark is produced by the spark plug to fire an air-fuel
mixture within the combustion chamber. In this mode, the starting target
air-fuel ratio is set to be rich, and the amount of the fuel to be
injected is increased.
If the coolant temperature WT exceeds the upper limit value WT2 (the second
predetermined temperature), which means that the engine coolant
temperature is sufficiently high, the starting target air-fuel ratio is
not set to be so rich, thus hardly causing overshoot of the engine speed
and deterioration of exhaust gas characteristics immediately after the
startup period. When the coolant temperature WT exceeds the upper limit
value WT2, too, the control flow goes to step S90 to sequentially inject
the fuel into all of the cylinders.
Next, step S50 is executed to determine whether the ambient temperature AT
detected by the ambient temperature sensor 54 is within a predetermined
range (AT1.ltoreq.AT), namely, whether the above-described condition (2)
is satisfied. If the ambient temperature AT is excessively low (i.e., if
the ambient temperature AT is equal to or lower than the lower limit value
AT1), the engine starting capability may be deteriorated by limiting the
number of cylinders to which the fuel is injected, even if the coolant
temperature WT does not fall below the lower limit value WT1. If an
affirmative decision (YES) is obtained in step S50, therefore, the control
flow goes to step S90 to inject the fuel into all of the cylinders in a
certain sequence.
Next, step S60 is executed to determine whether the engine speed Ne
calculated based on the detected information of the crank angle sensor 17
is equal to or lower than a predetermined speed Ne1 (that indicates the
finish of the startup period), namely, the above-described condition (3)
(Ne.ltoreq.Ne1) is satisfied or not. (This step corresponds to the engine
speed determining device.) If step S60 determines that the engine speed Ne
exceeds the predetermined speed Ne1 (that indicates the finish of the
startup period), the fuel control (enrichment of the air-fuel ratio)
performed during the engine startup is finished, and the control for
limiting the number of fuel injected cylinders is also finished.
In step S70, it is determined whether the time elapsed after the
commencement of cranking is within a predetermined period of time (the
counter value T of the timer 55 that starts measuring upon the start of
cranking is equal to or smaller than T1, or T T1). If the counter value T
is larger than T1, namely, if the engine speed Ne does not exceed the
predetermined speed Ne1 (that indicates the finish of the startup period)
even after the predetermined period of time T1 elapses, the engine
starting capability may deteriorate, and therefore the control for
limiting the number of fuel injected cylinders is stopped so as to assure
a sufficiently high engine starting capability. The control flow then goes
to step S90 to inject the fuel into all of the cylinders.
By contrast, if affirmative decisions (YES) are obtained in all of step S40
to S70, namely, all of the control conditions of these steps are
satisfied, the control flow goes to step S80 to perform a control
operation for limiting the number of cylinders into which the fuel is
injected. This control operation may be performed, for example, by 1)
initially injecting the fuel into the first cylinder, if it is determined
as the one into which the fuel can be timely injected upon completion of
cylinder identification, 2) stopping the fuel injection into the next
third cylinder, 3) injecting the fuel into the fourth cylinder in the same
manner as with the first cylinder, and 4) stopping the fuel injection into
the second cylinder in the same manner as with the third cylinder. Namely,
the fuel injection from the fuel injector valve 6 is inhibited with
respect to alternate ones of the cylinders. It is also to be noted that
the air-fuel ratio of each cylinder subjected to fuel injection is
controlled to be rich under the fuel control generally performed during
the engine startup.
After step S90 is executed, the control flow goes to step S100 to determine
whether the engine speed Ne is equal to or lower than the predetermined
speed Ne1 (that indicates the finish of the startup period). If the engine
speed Ne exceeds the predetermined speed Ne1, the fuel control during
engine startup (enrichment of the air-fuel ratio) is terminated, and the
control for limiting the number of fuel injected cylinders is also
terminated.
The air-fuel mixture supplied to the selected cylinders for which the fuel
injector valves are actuated under the above control for limiting the
number of fuel injected cylinders has an increased fuel concentration, as
in the case where the fuel is sequentially injected into all of the
cylinders, thus enabling the spark plug 4 to rapidly fire the mixture
without fail, without incurring deterioration of the engine starting
capability. Since the fuel injection is carried out with respect to only
the selected ones of the cylinders, the engine as a whole does not suffer
from overshoot of engine rotation, while assuring improved exhaust gas
characteristics and fuel efficiency.
FIG. 4(A) and FIG. 4(B) are graphs each showing changes in the engine speed
(Ne) and the amount of hydrocarbon (HC) discharged during engine startup,
in relation to the time measured from the commencement of cranking. FIG.
4(A) shows the case where the startup control apparatus of the present
embodiment was used, namely, where the starting target air-fuel ratio was
set to be rich, and the fuel is injected into only selected cylinders, and
FIG. 4(B) shows a conventional case where the starting target air-fuel
ratio is set to be rich, and the fuel is injected into all of the
cylinders. It will be understood from FIGS. 4(A) and 4(B) that the use of
the startup control apparatus of the present embodiment leads to reduced
overshoot of the engine speed and a more stable engine starting action, as
indicated by curve N1 compared to curve N2 showing the conventional case.
By comparing the amount of hydrocarbon (HC) discharged during engine
startup as indicated by curve H1 in FIG. 4(A) with that indicated by curve
H2 in FIG. 4(B), it will be understood that the HC amount (H1) discharged
from the engine of the present embodiment is significantly reduced with
respect to that (H2) from the conventional engine. In this connection, the
scaling of the vertical and horizontal axes of FIG. 4(A) is identical with
that of FIG. 4(B).
The graph of FIG. 5(A) shows a part of the graphs of FIGS. 4(A) and 4(B) in
enlargement, indicating the relationship between the engine speed
(vertical axis) and the time (horizontal axis), wherein P1 denotes a peak
value of the engine speed (curve N1) during engine startup when the
present startup control apparatus was used, and P2 denotes a peak value of
the engine speed (curve N2) during engine startup when the conventional
startup control apparatus was used. It will be understood from FIG. 5(A)
that the use of the startup control apparatus of the present embodiment
leads to a significant reduction in the overshoot of the engine speed
during engine startup, as indicated by curve N1, compared to the case
(curve N2) where the conventional control device is used.
When a negative decision (No) is obtained in step S70 of FIG. 3, and the
control flow goes to step S90, the engine speed Ne changes with time as
shown in FIG. 5(B). More specifically, where the fuel is injected into
only selected ones of the cylinders, the engine speed Ne normally
increases to exceed the predetermined speed Ne1 (that indicates the finish
of the startup period), by the time when a predetermined time T1 elapses
after the cranking switch is turned on, as indicated by curve N1. However,
if the engine speed Ne does not reach the predetermined speed Ne1 even
upon a lapse of the predetermined time T1 after the start of cracking, the
control device judges that the engine starting capability deteriorates
because the fuel is injected into only the selected ones of the cylinders,
and the fuel injection mode is switched to the one in which the fuel is
injected into all of the cylinders in a certain sequence, so as to
complete the engine starting action without fail. In this case, the engine
speed changes with time as indicated by curve N3.
It is to be understood that the present invention is not limited to the
illustrated embodiment, but may be otherwise embodied with various changes
or modifications, without departing from the principle of the present
invention.
In the illustrated embodiment, the fuel is initially injected into one of
the cylinders that is ready to receive the fuel upon completion of
cylinder identification, and the fuel injection into subsequent alternate
cylinders is stopped. It is, however, possible to initially inject the
fuel into a predetermined or fixed one of the cylinders upon completion of
cylinder identification. It is also possible to stop the fuel injection
into one of the cylinders that is ready to receive the fuel upon
completion of cylinder identification, and then stop the fuel injection
with respect to subsequent alternate ones of the cylinders.
While the fuel injection into alternate cylinders is stopped in the
illustrated embodiment, it is possible to stop the fuel injection with
respect to every two or more cylinders.
Furthermore, the startup control apparatus of the present invention may be
used in any type of engine, such as a series engine, a V-type engine, and
a horizontal opposed engine, including any number of cylinders that is
more than one.
While the present invention is effectively applied to an in-cylinder or
direct injection type engine that is surely able to control the fuel
injection into each cylinder as in the illustrated embodiment, the
invention is equally applicable to, for example, a multi-point fuel
injection (MPI) type engine in which fuel injector valves are provided at
intake ports, or other type of engine, provided that the fuel injection
can be effected with respect to each cylinder.
The present invention may also applied to internal combustion engines for
use in hybrid electric automobiles of series type or parallel type, and
internal combustion engines used for driving general vehicles.
In particular, the internal combustion engine of a hybrid electric
automobile is started and stopped in a repetitive manner, according to
changes in the battery capacity, and the frequency of starting and
stopping the engine is higher than that of ordinary internal combustion
engines. Thus, the present invention is most effectively applied to such
vehicles that repeat start and stop of the engine.
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